To study the mechanisms by which hair cells of vertebrate inner ears convert mechanical stimuli into electrical singnals, we will make intracellular recordings from individual hair cells while mechanical stimuli are applied directly to their hair bundles with fine glass probes. Voltage-clamp circuitry will be used to measure the membrane conductance of hair cells and its dependence upon hair bundle position. The cations in the saline solution bathing the apical cellular surface will be exchanged to learn which ions are able to carry transduction current. Hair bundles will be dissected to ascertain which organelles are required for transduction. The adaptation of the transduction apparatus to steady stimulation will be studied with intra- and extracellular recording techniques. The latency of the transducer's response and the kinetics of channel opening and closing will be investigated by extracellular recording of microphonics in preparations stimulated with very brief, rapid mechanical displacements. The pathological effects of aminoglycoside antibiotics on the transduction process of hair cells will be evaluated by intracellular recordings and with freeze-fracture electron microscopy. The action potential mechanism of hair cells, probably a calcium spike, will be studied to learn in which membrane surface it resides and whether it is associated with transmitter release and/or receptor potential amplification. The electrical relationship of hair cells with one another and with supporting cells will be studied both physiologically and anatomically.